1. Field of the Invention
The present invention relates to a flat panel display. More particularly, it relates to an electroluminescence display device that can increase the proportion of display area to substrate area and can reduce nonuniformity in luminance throughout the display area by reducing a voltage drop that can occur when supplying voltage to electrodes.
2. Description of the Related Art
In displaying an image, a variety of display devices are used and, in recent years, there have been numerous kinds of display devices available. Among these display devices, the organic electroluminescent device (a flat emissive-type display device that does not require a separate emission device such as a backlight) has become popular because it enables highly efficient operation with low power consumption and is capable of blue emission.
The electroluminescence display device utilizes the light emission principle in which, when an electric field is applied between the two electrodes, electrons are injected from the cathode side and holes are injected from the anode side. The electrons are recombined with the holes in the light emitting layer to form an excited state and energy generated when the excited state returns to the ground state is emitted as light.
In an electroluminescence display device, an organic electroluminescent portion includes several layers stacked on a substrate, including a first electrode, that is, an anode, an organic light-emitting portion, and a second electrode, that is, a cathode. The organic light-emitting portion includes an organic emission layer (EML), in which recombination of holes and electrons occurs to form excitons and generate light.
In order to increase emission efficiency, it can be useful to facilitate migration of holes and electrons to an organic emission layer. To this end, an electron transport layer (ETL) may be disposed between the cathode and the organic emission layer, and a hole transport layer (HTL) may also be disposed between the anode and the organic emission layer. Also, a hole injection layer (HIL) may be disposed between the anode and the HTL, and an electron injection layer (EIL) may be disposed between the cathode and the ETL.
There are passive matrix-type (PM) and active matrix-type (AM) organic electroluminescence displays. The passive-matrix type EL device may be simply constructed such that anodes and cathodes are arranged in columns and rows. Scanning signals can be supplied to the cathodes from a row driver. A single row can be selected from a plurality of rows. Data signals can be applied to each pixel from a column driver. The active matrix type EL device controls signals input to each pixel using thin film transistors (TFTs) and is suitable for processing a large quantity of signals, and thus is widely used as a motion picture display device.
In an organic/inorganic electroluminescent display device, particularly, in an active matrix type organic/inorganic electroluminescent device, a problem is presented that a proportion of a display area including pixels relative to a substrate is reduced due to lay-out of various driving circuits and wirings substrate.
FIG. 1A is a plan view of a general active matrix type electroluminescence display device. FIG. 1B is a cross-sectional view taken along the line I-I shown in FIG. 1A.
The active matrix type electroluminescence display device shown in FIGS. 1A and 1B includes a predetermined display area 20 having an organic electroluminescent device on a transparent insulating substrate 10. In order to seal the display area 20, a metal cap 90 may be sealed by a sealing portion 80 having a sealing member 81.
The organic electroluminescent device including thin film transistors has a plurality of pixels arranged in the display area 20 and a cathode electrode 40 disposed on the display area 20. The cathode electrode 40 can be connected to an external terminal region 70 through an electrode wiring portion 41 provided at one side of the display area 20. Also, the display area 20 can have a plurality of driving lines (VDD) 31 arranged thereon. The driving lines 31 are connected to the terminal region 70 through a driving power wiring portion 30 outside the display area 20, and supply driving power to the display area 20. Also, a vertical circuit portion 50 and a horizontal circuit portion 60 for applying signals to TFTs of the display area 20 are further provided outside the display area 20, and are both connected to the terminal region 70 by circuit wiring portions 51 and 61, respectively.
In the aforementioned active matrix type electroluminescence display device, the metal cap 90 as a sealing member seals the entire region excluding the terminal region 70, including the wiring portions 51 and 61 and the circuit portions 50 and 60 as well as the display area 20. As a result, the sealing portion 80 encapsulates not only the display area 20, which is an image display portion, but also a non-image display portion, that is, the wiring portions 51 and 61 and the circuit portions 50 and 60. This lowers a proportion of the display area 20 relative to the overall size of the display device, resulting in an increase in dead space (i.e. non-emissive region).
The above-noted problems are described in Korean Patent Publication No. 2001-83213. Here, a protective electrode as a cathode is connected to an external FPC through a wiring structure disposed at the edge of a sealing portion, occupying a considerable area of the edge of the sealing portion.
To overcome such a lay-out problem, the electroluminescence display device shown in FIGS. 1A and 1B is constructed such that a width of the wiring portion 51, 61 that connects the display area 20 and the terminal region 70 is reduced. This design, however, increases resistance of the wiring portion 51, 61, resulting in deterioration of luminance.
Japanese Patent Publication No. 2003-316284 discloses a liquid crystal display device with a reduced panel size, in which liquid crystals are injected between a substrate having common electrodes arranged thereon and a substrate having pixel electrodes arranged thereon to then be sealed. A gap between the substrates provided for injection of the liquid crystals may cause a step difference between the common electrodes and power supply lines for supplying power to the common electrodes, and disconnection between the common electrodes and the power supply lines may occur due to such a step difference. This disconnection may result in a considerable voltage drop, leading to deterioration of luminance in the display area.